1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device and a method for fabricating the same, which reduces the amount of liquid crystal material used in the liquid crystal display device in accordance with a particular column spacer formation process.
2. Background of the Related Art
With the progress of an information-dependent society, the demand for various display devices has increased. To meet such demands, efforts have recently been made to research flat panel display devices such as liquid crystal display (LCD) devices, plasma display panels (PDPs), electro-luminescent display (ELD) devices, vacuum fluorescent display (VFD) devices, and the like. Some types of such flat panel display devices are being practically applied to various appliances for display purposes. In particular, LCDs have been increasingly substituted cathode ray tubes (CRTs) in mobile image display devices because LCDs have superior picture quality, low weight, thin profile, and low power consumption. Thus, LCDs are currently most widely used for mobile image display devices. Various applications of LCDs are being developed in association with not only mobile image display devices, such as monitors of notebook computers, but also monitors of TVs to receive and display broadcasting signals, and monitors of laptop computers. Successful application of such LCDs to diverse image display devices depends on whether or not the LCDs can realize the desired high picture quality including high resolution, high brightness, large display area, and the like, while maintaining the desired characteristics of light weight, thin profile, and low power consumption.
Hereinafter, a related art LCD device will be described with reference to the annexed drawings.
FIG. 1 is an exploded perspective view illustrating a related aft twisted nematic (TN) mode LCD device. As shown in FIG. 1, the related art TN mode LCD device includes a first substrate 1 and a second substrate 2 assembled onto each other such that a certain space is defined between the first and second substrates 1 and 2. The LCD device also includes a liquid crystal layer 3 sealed in the space between the first and second substrates I and 2. The structure including all the first substrate 1, second substrate 2 and liquid crystal layer 3 is called a “liquid crystal panel.”
The structure of the LCD device will now be described in more detail. The first substrate I includes a plurality of gate lines 4 arranged in one direction while being uniformly spaced apart from one another, and a plurality of data lines 5 arranged in a direction perpendicular to the gate lines 4 while being uniformly spaced apart from one another. The gate lines 4 and data lines 5 define pixel regions P. Pixel electrodes 6 are arranged on the first substrate 1 at respective pixel regions P. Thin film transistors T are formed at intersections of the gate lines 4 and data lines 5, respectively. Each thin film transistor T applies a data signal on an associated one of the data lines 5 to an associated one of the pixel electrodes 6 in accordance with a signal on an associated one of the gate lines 4. The second substrate 2 includes a black matrix layer 7 for blocking incidence of light to regions other than the pixel regions P. The second substrate 2 also includes R, G, and B color filter layers 8 respectively formed at regions corresponding to the pixel regions P, and adapted to express color tones, and a common electrode 9 formed to cover the color filters 8, and adapted to render an image. At each pixel region P, the liquid crystal layer 3 interposed between the first and second substrates 1 and 2 is oriented in accordance with an electric field generated between the associated pixel electrode 6 and the common electrode 9. In accordance with the orientation degree of the liquid crystal layer 3, the amount of light passing through the liquid crystal layer 3 is determined. Thus, a corresponding image can be expressed. Although not shown, ball spacers or column spacers are formed between the first and second substrates 1 and 2, to maintain a cell gap for the liquid crystal layer 3.
Such an LCD device is called a “TN mode LCD device.” Since a TN mode LCD device has a drawback of a narrow viewing angle, an in-plane switching (IPS) mode LCD device has been developed to overcome the drawback of the TN mode LCD device. Hereinafter, a related art IPS mode LCD device, which is driven in an IPS mode, will be described. FIG. 2 is a plan view illustrating a related art IPS mode LCD device. FIG. 3 is a cross-sectional view taken along the line I-I′ of FIG. 2. As shown in FIGS. 2 and 3, the related art IPS mode LCD device mainly includes a first substrate 30, a second substrate 40 assembled onto the first substrate 30 such that a certain space is defined between the first and second substrates 30 and 40, and a liquid crystal layer 55 sealed between the two substrates 30 and 40. The structure including all the first substrate 30, second substrate 40, and liquid crystal layer 55 is called a “liquid crystal panel.” The related art IPS mode LCD device has the same structure as the above-mentioned general LCD device of FIG. 1, except that an overcoat layer is substituted for the common electrode of the second substrate in the general LCD device.
This structure will now be described in more detail. In the related art IPS mode LCD device, gate lines 31 and data lines 32 are arranged in an array region on the first substrate 30 such that the gate lines 31 and data lines 32 intersect each other, to define pixel regions. TFTs are formed at respective intersections of the gate lines 31 and data lines 32. In each pixel region, pixel electrodes 33 and common electrodes 35a are alternately formed. The common electrodes 35a extend in a direction parallel to the gate lines 31 while being branched from a common line 35 formed on the same layer as the gate lines 31. Each TFT includes a gate electrode 31a protruded from the associated gate line 31, a semiconductor layer 34 covering the gate electrode 31a, and a source electrode 32a and a drain electrode 32b formed at opposite sides of the semiconductor layer 34, respectively. The source electrode 32a protrudes from the associated data line 32. The drain electrode 32b is spaced apart from the source electrode 32a by a predetermined distance. A gate insulating film 36 is also formed over the resultant surface of the first substrate 30 including the gate lines 31 and common lines 35 to insulate the metal lines from each other. A passivation film 37 is formed over the gate insulating film 36 including the data lines 32. The second substrate 40, which faces the first substrate 30, includes a black matrix layer 41 for shielding non-pixel regions (gate line, data line and TFT regions) other than the pixel regions, color filter layers 42 respectively formed in the pixel regions while sequentially and repeatedly containing R, G, and B pigments. A plurality of column spacers 50 are formed in desired regions on the overcoat layer 43, to maintain a desired cell gap between the first and second substrates 30 and 40. The column spacers 50 are arranged uniformly spaced apart from one another while corresponding to the gate lines 31. When the first and second substrates 30 and 40 are assembled, the column spacers 50 support the first and second substrates 30 and 40 such that a desired cell gap is maintained between the first and second substrates 30 and 40.
As mentioned above, in both the related art TN mode LCD device and the related art IPS mode LCD device, the space between the facing first and second substrates is adjusted through the above-mentioned column spacers. However, all the column spacers, which are adapted to maintain a desired cell gap, have the same structure, and the structure of the column spacers is simply shaped to correspond to the cell gap between the first and second substrates. For this reason, there is a problem in a touch operation for a test; in which the surface of one of the first and second substrates is rubbed in a certain direction. That is, there may be defects caused by the touch operation in that the substrate cannot be rapidly recovered from a shifted state to an original state, or a depression stain such as a trace is formed in a region where a pressure is locally applied to the substrate. Thus, various luminous defects may be observed after the touch operation. In addition, although liquid crystals are filled in a space between the first and second substrates, the filling of the liquid crystals causes a large burden in terms of process time and expense.
The above-described related art LCD devices have the following problems. Since liquid crystals should be completely filled in a space between the first and second substrates, except for the column spacers adapted to maintain a desired vertical gap between the first and second substrates, a large amount of liquid crystal material is needed. In association with the manufacture of panels, in particular, efforts to reduce the use amount of liquid crystal materials have been made because the use of liquid crystals causes a large burden in terms of process time and expense. Furthermore, with an LCD device including column spacers configured to simply maintain a desired vertical gap between the first and second substrates, display defects may be generated in a test involving a touch operation, in which the surfaces of the substrates are rubbed, or local application of a pressure to the substrates.